Wi-Fi is the most ubiquitous wireless networking protocol, but the excessive power consumption of Wi-Fi radios has limited their adoption into the rapidly growing class of ultra-low power (ULP) IoT devices. This is because the Wi-Fi requirements are not suitable for ULP implementations, and to date no <10 mW Wi-Fi receiver has been reported. Ideally an ULP IoT device would have an active network connection, however with Wi-Fi this results in continuously turning on the radio to keep the device associated with a router, limiting power savings from duty-cycling. ULP wake up radios could be used to address this problem, but these require custom signals not supported by Wi-Fi networks, limiting their widespread adoption. To close this gap, a messaging technique is developed as a back-channel that uses a Wi-Fi standard-compliant transmitter to produce a signal that can be detected by an ULP FSK receiver.
This disclosure presents a complete 335 μW ULP receiver able to demodulate FSK back-channel messages that are embedded in standard-compliant Wi-Fi packets. On the Wi-Fi router, generating back-channel messages only requires control of the payload data in a single packet, therefore it is supported by any 802.11a or later router and suitable for widespread adoption. By modulating the payload of a Wi-Fi packet, a wideband, binary FSK-modulated back-channel message is produced via the OFDM symbols. The ULP receiver then detects the FSK modulated back-channel message. This wideband FSK message relaxes several specifications of the ULP receiver such as phase distortion, order of the filter, and inter-modulation, which helps to reduce receiver power. The receiver down-converts the RF signal with the 3rd harmonic term of commutating mixer. This reduces power consumption of the local oscillator (LO), enabling a wide band 5.8 GHz receiver at sub-mW.
This section provides background information related to the present disclosure which is not necessarily prior art.